Traditionally, an electrical connection between each of a plurality of metallized areas on one substrate, (i.e., a circuit board) and each of a plurality of areas on another substrate has been accomplished by way of one or more cables. Typically, each cable has each of its ends terminated with a connector adapted to mate with a corresponding connector on each circuit board. The disadvantage with this approach is that the cost associated with the connectors is relatively high, as is the effort required to install each connector at each cable end. For this reason, much effort is being devoted to exploring lower cost interconnection alternatives.
Instead of using cables, an electrical connection between the metallized areas on one circuit board and those on the other can be accomplished by arranging the boards in opposing relationship and then sandwiching one or more layers of anisotropically conductive material between them. The anisotropically conductive material used for this purpose is characterized by very good electrical conductivity along its thickness (z axis) direction but very poor electrical conductivity throughout its bulk (x-y) direction. Anisotropically conductive materials having this property are typically manufactured by arranging a plurality of electrically conductive members, (i.e., wires or chains of conductive particles) in a non-conductive matrix (i.e., silicone rubber or the like) so that the conductive members extend along the z axis in spaced relationship from each other. In this way, the conductive members in the non-conductive matrix provide a plurality of conductive paths in the z-axis direction only.
To maintain a good electrical connection between the metallized areas on the opposed circuit boards, the layer of anisotropically conductive material sandwiched between the boards must be uniformly compressed. To this end, one or more mechanical fasteners (e.g., screws, bolts or heat-staked pins) extend through the two circuit boards to compress the anisotropically conductive material interposed between the boards. In the past, uniform compression of the regions of the anisotropically conductive material in contact with the metallized areas on each of the opposing circuit boards has been difficult to obtain. The metallized areas on each circuit board are typically arranged in a square or rectangular array, whereas each fastener exerts concentric rings of constant pressure. Thus, unless a very large number of fasteners are employed (which increases the cost and difficulty of assembly), each region of the anisotropically conductive material in contact with a metallized area lying outside a constant pressure ring associated with a particular fastener will be subjected to less compression than the metallized areas within such a ring.
Therefore, there is a need for an interconnection technique which provides for more uniform compression of those regions of anisotropically conductive material in contact with the arrays of metallized areas on opposing circuit boards.